Attenuation of urinary sodium excretion during cold-air exposure in trained athletes

To clarify whether an increase in urinary sodium (Na) excretion during cold-air exposure is attenuated in trained athletes, we analyzed the urinary and hormonal responses to cold-air exposure at 15°C in trained (TR, n=9) and untrained men (UT, n=9). During 15°C exposure in the UT group, the urinary Na excretion (U(Na)V), fractional excretion of Na and urinary Na to K ratio (U(Na/K)) increased significantly (p<0 01-0.05), but there were no variations in creatinine clearance or the filtered Na load. In the TR group, however, no significant changes were demonstrated in these parameters. The amount of increase in plasma noradrenaline and of decrease in plasma volume were greater, and the ADH and adrenaline responses were smaller in the TR group than those found in the UT group during 15°C air exposure. A significant positive correlation was demonstrated between the increase of U(Na)V and both the relative changes of U(Na/K) and mean blood pressure. These results indicated that natriuresis during cold-air exposure was induced by the decrease in tubular reabsorption of Na, and that natriuresis was attenuated in trained athletes.